1. Field of the Invention
The present invention relates generally to a method and system for transmitting data in a mobile communication system, and in particular, to a method and system for controlling a rate of data transmitted in a reverse direction.
2. Description of the Related Art
Generally, 2nd generation (2G) Code Division Multiple Access (CDMA) mobile communication systems provide voice service with low-speed data service through a traffic channel in forward and reverse directions. With the rapid progress of wireless technology, increased amounts of data need to be transmitted at high speeds to provide users with multimedia content and Internet access in addition to simple voice service. To meet user demand, mobile communication systems are developing into advanced systems capable of providing both high-speed data service and voice-oriented service.
The 3rd generation (3G) mobile communication system aims at providing high-speed service with a special focus on data-oriented multimedia service.
For example, a 1x Evolution-Data Only (EV-DO) standard, also known as High Data Rate (HDR), has been established by 3rd Generation Partnership Project 2 (3GPP2) which is a standardization camp for a synchronous system with the intent to provide a CDMA2000 1x data service. During forward transmission, a 1x EV-DO system transmits packet data to a particular mobile station only. Therefore, the 1x EV-DO system can transmit packet data to the particular mobile station with maximum power at high speed.
A description will now be made of the 1x EV-DO system. For a forward link of the 1x EV-DO system, an access network (AN) or a base station (BS) serves as a transmitter while an access terminal (AT) or a mobile station (MS) serves as a receiver. A physical layer of the 1x EV-DO system adopting a link adaptation scheme adaptively uses various modulation schemes such as Quadrature Phase Shift Keying (QPSK), 8-ary Phase Shift Keying (8PSK) and 16-ary Quadrature Amplitude Modulation (16QAM), with various data rates according to a channel environment. In addition, the 1x EV-DO system supports multimedia service using the same frequency band, and in the system, a plurality of mobile stations can simultaneously transmit data to a base station. In this case, identification of the mobile stations is achieved through spreading codes uniquely allocated to the mobile stations.
In the 1x EV-DO system, data transmission in a reverse direction from a mobile station to a base station is achieved through a reverse packet data channel (R-PDCH) per physical layer packet (PLP), with a fixed packet length. The data rate for each packet is variable, and is based on the power of the receiving mobile station to which a corresponding packet is transmitted, the total amount of data to be transmitted to the mobile station, and information provided from a base station.
While a mobile station attempts to change its connection from a current base station (or serving base station) to a new base station (or target base station) to perform handoff or to set up initial communication, the mobile station cannot receive rate control information from the target base station because the connection to the target base station is not established. Therefore, the mobile station has difficulty in efficiently controlling the rate of transmission for each data packet according to channel conditions.